Conventional recording media for recording music data, image data, or data for use in a computer or the like include a disc-shaped recording medium (hereinafter will be referred to as “disc”), such as a CD or a DVD. Such discs include not only read-only discs but also, for example, once-writable discs and repeatedly rewritable discs.
Such a disc has a single or plural thin film layers deposited on a surface of a disc-shaped disc substrate having an opening portion defined centrally thereof. Such a thin film layer is deposited by sputtering for example.
In depositing a thin film layer on the surface of the disc substrate, initially, the disc substrate fed from the outside of a sputtering system is carried into the sputtering system. At that time, the disc substrate is carried into the sputtering system by a disc substrate carrying-in and carrying-out section (which is also called “disc substrate transfer unit”) provided in the sputtering system. The disc substrate carrying-in and carrying-out section also carries out the disc substrate having the thin film deposited thereon by the sputtering system to the outside of the sputtering system.
At that time, the conventional disc substrate carrying-in and carrying-out section picks up the disc substrate fed from, for example, a disc exchange unit located outside the sputtering system by holding the opening portion defined centrally of the disc substrate with a bore chuck and then moves the disc substrate to a carry-in entrance provided at a thin film depositing section of the sputtering system. Thereafter, with a disc receiving tray inside the sputtering system being previously placed adjacent the carry-in entrance, the bore chuck is released to pass the disc substrate to the disc receiving tray, thereby completing the carrying-in of the disc substrate.
When carrying out the disc substrate having the thin film deposited thereon, the disc receiving tray mounting the disc substrate having the thin film deposited thereon is previously placed adjacent the carry-in entrance and then the disc substrate is picked up by holding the opening portion defined centrally of the disc substrate with the bore chuck of the disc substrate carrying-in and carrying-out section. Thereafter, the disc substrate thus picked up is moved to the disc exchange unit and then the bore chuck is released to pass the disc substrate to the disc exchange unit, thereby completing the carrying-out of the disc substrate.
However, since the thin film is deposited by the sputtering system usually under a high temperature condition, the disc substrate is thermally deformed. For this reason, when, for example, the disc substrate is solely carried out of the sputtering system, time is required to cool the disc substrate in order to prevent the bore chuck from mischucking due to thermal deformation of the opening portion of the disc substrate. As a result, a problem arises that the availability factor lowers.
As a method for solving such a problem, there is, for example, a method including feeding the disc substrate as mounted on a substrate holder which is less susceptible to thermal deformation than the disc substrate and carrying the substrate holder mounting the disc substrate into the sputtering system.
In depositing the thin film on the surface of the disc substrate, it is a general practice to cover the periphery of the opening portion defined centrally of the disc substrate and an outer peripheral portion of the disc substrate with an inner mask and an outer mask, respectively, and then deposit the thin film annularly in a region covered with neither the inner mask nor the outer mask. At that time, it is also a general practice for the conventional sputtering system to place the inner mask and the outer mask on the surface of the substrate within the sputtering system. As a method for placing the inner mask and the outer mask on the surface of the substrate, there is, for example, a method including providing a mask column functioning as the inner mask on a central portion of a target and the outer mask on an outer peripheral portion of the target and then bringing the surface of the disc substrate into contact with the mask column and the outer mask (see Patent Document 1 for example).
Other methods include, for example, a method including: providing a mask transfer section inside the sputtering system; placing the inner mask and the outer mask on the surface of the disc substrate halfway through movement of the disc substrate and substrate holder carried into the sputtering system to a sputtering position; and removing the inner mask and outer mask placed on the surface of the disc substrate halfway through movement of the disc substrate having the thin film deposited thereon and the substrate holder to a carrying-out position (see Patent Document 2 for example).    Patent Document 1: Japanese Patent Laid-Open No. 2002-25132    Patent Document 2: Japanese Patent Laid-Open No. 2002-47555
With the sputtering system for use in the manufacture of a conventional CD or DVD, however, it is a general practice to place the inner mask and the outer mask on the surface of the substrate within the sputtering system.
Discs including such a DVD have been improved in recording density in recent years and hence call for an ultrafine structure, a high density, and high precision. For this reason, a film deposition region for the thin film to be deposited on the disc substrate also calls for high precision. That is, the sputtering system for depositing the thin film on the disc substrate calls for high precision positioning of the inner and outer masks relative to the disc substrate. It takes time for such positioning (i.e., centering setup) to be achieved. Particularly, a repeatedly rewritable DVD, such as DVD-RAM (DVD-Random Access Memory) or DVD-RW (ReWritable), has multilayer thin films and, hence, it takes time for the positioning of the inner and outer masks to be achieved before deposition of each thin film. Thus, a problem exists that the availability factor and the disc productivity lower.
In depositing the thin film on the surface of the disc substrate by the sputtering system, the thin film is deposited also on the surfaces of the inner and outer masks. For this reason, maintenance is necessary for periodically cleaning the inner and outer masks. However, since the conventional sputtering system of the common type has the inner and outer masks placed inside a vacuum chamber (i.e., thin film depositing section), a problem exists that the operation for removing the inner and outer masks before cleaning and the operation for mounting the inner and outer masks after cleaning are troublesome and, hence, it takes time to complete these operations.
In recent years, a method of fixing the inner mask and the outer mask to the substrate holder by utilizing a magnet, has been proposed which is applicable to the sputtering system for depositing the thin film on the surface of the disc substrate (see Japanese Patent Laid-Open No. 2003-303451 for example). This method includes fixing the inner mask and the outer mask to the disc substrate mounted on the substrate holder, for example, at a place outside the sputtering system and then carrying the disc substrate kept in this state into the sputtering system. The method, however, involves a problem that a mechanism is necessary for fixing the inner and outer masks to the disc substrate during the carrying-in operation and removing the inner and outer masks during the carrying-out operation.
An object of the present invention is to provide a technique which is capable of facilitating high precision positioning of the inner mask and outer mask in a sputtering system for depositing a thin film on a surface of a disc-shaped disc substrate.
Another object of the present invention is to provide a technique which is capable of facilitating maintenance of the inner mask and outer mask in the sputtering system for depositing a thin film on a surface of a disc-shaped disc substrate.
Another object of the present invention is to provide a technique which is capable of facilitating high precision positioning of the inner mask and outer mask, facilitating maintenance, and simplifying the system configuration in the sputtering system for depositing a thin film on a surface of a disc-shaped disc substrate.
The foregoing and other objects and novel features of the present invention will become apparent from the description of the present invention and the attached drawings.